Dental caries affects people of all ages and is a worldwide health concern. Streptococcus mutans is a major cariogenic bacterium because of its ability to form biofilm and induce an acidic environment. In this study, the antibacterial activities of magnolol and honokiol, the main constituents of the bark of
magnolia plants, toward planktonic cell and biofilm of S. mutans were examined and compared with those of chlorhexidine. The minimal inhibitory concentrations of magnolol, honokiol and chlorhexidine for S. mutans were 10, 10 and 0.25mg/mL, respectively. In addition, each agent showed bactericidal
activity against S.mutans planktonic cells and inhibited biofilmformationin a dose- andtime-dependent manner.Magnolol (50mg/mL) had greater bactericidal activity against S. mutans biofilm than honokiol (50mg/mL) and chlorhexidine (500mg/mL) at 5min after exposure, while all showed scant activity
against biofilm at 30 s. Furthermore; chlorhexidine (0.5–500mg/mL) exhibited high cellular toxicity for the gingival epithelial cell lineCa9-22 at 1 hr,whereasmagnolol (50mg/mL) and honokiol (50mg/mL) did not. Thus; it was found thatmagnolol has antimicrobial activities against planktonic and biofilm cells of S. mutans. Magnolol may be a candidate for prevention and management of dental caries.